This paper presents the optimal design of an electromagnetic vibration-based generator using the simulated annealing method (SA). To optimally extract the vibrational energy of a system vibrating at a specific frequency, the selected mass and spring stiffness of a resonant vibration is required. The relationship between induced energy and the generator's structure, its permanent magnet height and diameter, number of turns, and wire diameter in a single air coil are discussed. Also, a prototype of the vibrationbased electrical generator is built and tested via a shaker excited at resonance frequency and input amplitude of 0.06mm. Consequently, results reveal that the design parameters (permanent magnet height and diameter, number of turns, and wire diameter) play essential roles in maximizing electrical power.

The paper is an exploration of the optimal design parameters of a space-constrained electromagnetic vibration-based generator. An electromagnetic energy harvester is composed of a coiled polyoxymethylen circular shell, a cylindrical NdFeB magnet, and a pair of helical springs. The magnet is vertically confined between the helical springs that serve as a vibrator. The electrical power connected to the coil is actuated when the energy harvester is vibrated by an external force causing the vibrator to periodically move through the coil. The primary factors of the electrical power generated from the energy harvester include a magnet, a spring, a coil, an excited frequency, an excited amplitude, and a design space. In order to obtain maximal electrical power during the excitation period, it is necessary to set the system’s natural frequency equal to the external forcing frequency. There are ten design factors of the energy harvester including the magnet diameter (D_m), the magnet height (H_m), the system damping ratio (ζ_sys), the spring diameter (D_s), the diameter of the spring wire (d_s), the spring length (ℓ_s), the pitch of the spring (p_s), the spring’s number of revolutions (N_s), the coil diameter (D_c), the diameter of the coil wire (d_c), and the coil’s number of revolutions (N_c). Because of the mutual effects of the above factors, searching for the appropriate design parameters within a constrained space is complicated. Concerning their geometric allocation, the above ten design parameters are reduced to four (D_m, H_m, ζ_sys, and N_c). In order to search for optimal electrical power, the objective function of the electrical power is maximized by adjusting the four design parameters (D_m, H_m, ζ_sys, and N_c) via the simulated annealing method. Consequently, the optimal design parameters of D_m, H_m, ζ_sys, and N_c that produce maximum electrical power for an electromagnetic energy harvester are found.

Recently, research on new techniques for single-chamber mufflers equipped with perforated resonating tubes has been addressed. However, the acoustical performance of mufflers having a narrow-band sound transmission loss (STL) is insufficient in reducing a broadband venting noise. To improve the acoustical efficiency, a hybrid muffler with chambers composed of perforated intruding inlets is presented. Here, we will not only analyze the STL of three kinds of mufflers (A: a one-chamber muffler hybridized with a perforated resonating tube; B: a two-chamber muffler hybridized with a perforated intruding tube and a resonating tube; and C: a three-chamber muffler hybridized with two perforated intruding tubes and a resonating tube), but also optimize the best design shape within a space-constrained situation. In this paper, both the numerical decoupling technique and simulated annealing (SA) for solving the coupled acoustical problem of perforated tubes are used. A numerical case for eliminating a broadband air compressor noise is also introduced. To verify the reliability of SA optimization, optimal noise abatements for the pure tones (400 Hz and 800 Hz) are exemplified. Before the SA operation can be carried out, the accuracy of the mathematical model is checked using the experimental data. Results indicate that the maximal STL is precisely located at the desired target tones. The optimal result of case studies for eliminating broadband noise also reveals that the overall noise reduction with respect to the mufflers can be reduced from 131.6 dB(A) to 102.1 dB(A), 89.5 dB(A), and 82.1 dB(A). As can be seen, the acoustical performance will increase when the diameters (at the inlet tubes as well as perforated holes) decrease. Moreover, it is obvious that the acoustical performance will be improved when the chambers equipped with perforated intruding inlets are increased. Consequently, a successful approach used for the optimal design of the multichamber mufflers equipped with perforated intruding tubes and a resonating tube within a space-constrained condition has been demonstrated.